Conformation of poly-L-tyrosine in aqueous solution

The conformational transition of poly-L -tyrosine in 0.1M KCl was investigated by ORD and infrared spectroscopy, potentiometric titration, and sedimentation velocity experiments. It is shown that the fully ordered conformer is obtained by slow titration of the random coil with 0.1N HCl at 25°C. The charge-induced transition, at variance with other poly-α-amino acids, is completed in a narrow range of α. An aggregation process was detected both by potentiometric titration and sedimentation velocity. The polyamino acid aggregates around α = 0.7 at 25°C when the conformational transition is almost complete. Infrared spectra, in the region of the amide I band (1650 cm^?1) showed that the transition is a random coil → antiparallel β one. Evidence exists that the form is of the intramolecular type. The foregoing interpretations of ORD and CD spectra in terms of the α-helix conformation are discussed.